In a liquid rocket engine, an injector is a component that mixes and injects the fuel and oxidizer into the combustion chamber. The injector plays a critical role in the combustion process, as it must ensure that the fuel and oxidizer are mixed in the correct proportions and distributed evenly across the combustion chamber.
The injector typically consists of a number of small orifices or nozzles that are arranged in a specific pattern to achieve the desired mixing and distribution. The process of mixing the propellants is known as atomization.
There are many various types of injectors. Each different type has a tradeoff between efficiency, throttleability, and manufacturability.
On all injectors, there are an array of elements - the arrangement of these elements can affect the performance of the injector.
Additionally, the element type will affect the performance of the injector
The showerhead injector is among the simplest types of injectors. Each element consists of a hole for fuel drilled parallel to a hole for oxidizer.
Showerhead injectors do not atomize very well, and have many other disadvantages. However, their ease of manufacturability makes them a popular choice for amateurs.
Shown below is a diagram of a showerhead injector element:
By angling the boreholes for the propellants, atomization can be achieved with the physical collision of the propellant streams. This injector configuration is known as an impinging jet.
Two common variations of the impinging jet injector is the doublet and triplet element configuration. A doublet configuration allows a collision between two propellant streams, and a triplet configuraiton allows a collision between three propellant streams.
These configurations can be either "like" or "unlike." A "like" configuration means that the colliding streams are the same propellant, and "unlike" streams are collisions between different propellants, with potentially different mass flow rates or densities.
These element configurations lead to a much more efficient reaction in the combustion chamber.
There are several other types of element configurations, such as a quadlet or pentad arrangement.
Instead of allowing the streams to collide with themselves, a splash plate injector uses a plate to atomize the propellants.